1. Field of the Invention
This invention relates to a sealing structure of a cell tube of tubular type fuel cell, which increases sealability of the cell tube to enhance the electrical characteristics of the fuel cell.
2. Description of the Related Art
FIG. 3 outlines the structure of a tubular type solid electrolyte fuel cell module. FIG. 4 is a perspective schematic view of a cell tube portion of the module. FIG. 5 is a schematic structural view of a sealing structure at the end of the cell tube.
As shown in FIG. 3, a top plate 02, an upper tube sheet 03 and a lower tube sheet 04 are disposed in a module body 01 surrounded by a heat insulator. Below the lower tube sheet 04, a cell chamber 01a is formed. Between the top plate 02 and the upper tube sheet 03 of the module body 01, a fuel supply chamber 05 is formed. Between the upper tube sheet 03 and the lower tube sheet 04, a fuel discharge chamber 06 is formed. To the top plate 02 of the fuel supply chamber 05, an external pipe 07 for establishing communication between the fuel supply chamber 05 and the outside of the module body 01 is connected in such a manner as to pass through the module body 01. Inside of the external pipe 07, an internal pipe 08 passing through the upper tube sheet 03 is disposed for establishing communication between the fuel discharge chamber 06 and the outside of the module body 01.
Cell tubes 010, each comprising unit cell films (not shown) formed on an outer peripheral surface thereof, pass through and are supported by the lower tube sheet 04 such that the upper end of the cell tube 010 is positioned in the fuel discharge chamber 06, and that a lower portion of the cell tube 010 is positioned in the cell chamber 01a of the module body 01. Inside the cell tube 010, a fuel injection pipe 011 passing through the upper tube sheet 03 is disposed for establishing communication between the inner lower portion of the cell tube 010 and the interior of the fuel supply chamber 05. Inside the injection pipe 011, a current collecting rod 012 is disposed which has an upper end positioned in the fuel supply chamber 05 and a lower end positioned near the lower end of the cell tube 010. The lower end of the current collecting rod 012 is coupled to a current collecting member 013 which is electrically connected to the above-mentioned unit cell films and which closes the lower end of the cell tube 010. The upper end of the current collecting rod 012 is electrically connected to the outside of the module body 01 via a current collecting member 013 of nickel and a conductive rod 014.
To the upper end of the cell tube 010, a current collecting connector 015 electrically connected to the unit cell films is attached. The current collecting connector 015 is series connected to other cell tubes 01 via the same current collecting connectors 015.
In a lower portion of the cell chamber 01a of the module body 01, a partition plate 016 of a porous ceramic material is provided. Below the partition plate 016, an air preheating chamber 017 communicating with the cell chamber 01a via the partition plate 016 is provided. To the air preheating chamber 017, an air supply pipe 018 communicating with the outside of the module body 01 is connected. Inside the cell chamber 01a of the module body 01, an end of an air discharge pipe 019 is located. The air discharge pipe 019 has the other end located outside the module body 01, and its intermediate portion is disposed in such a manner as to pass through the interior of the air preheating chamber 017 for the purpose of heat exchange.
The cell tube 010 suspended from the lower tube sheet 04 of the module body 01, as shown in FIGS. 4 and 5, is formed by laminating a fuel electrode 032a, an electrolyte 032b, and an air electrode 032c in this order on a surface of a substrate tube 031, and further laminating a dense conductive connecting material (interconnector) 033 for connecting the fuel electrode and the air electrode. In this manner, a plurality of unit cell films 032 are formed in a lateral-striped pattern. That is, the unit cell film 032 is constituted by the fuel electrode 032a, the solid electrolyte 032b, and the air electrode 032c laminated on the substrate tube 031. The interconnectors 033 each seal the interface between the inside and the outside of the substrate tube 031 in the space between the unit cell films 032, thus connecting the unit cell films 032 in series.
The film configuration of a sealed portion of the foregoing cell tube 010 will be described with reference to FIGS. 5 and 6.
As shown in FIGS. 5 and 6, a lead film (Nixe2x80x94Al) 034 connected via the interconnector 033 to the air electrode 032c and located on the outer surface of the substrate tube (15%CaOxe2x80x94ZrO2) 031 is formed on the outer peripheral surface of a lower end portion of the substrate tube 031. The lead film 034 is provided with a current collecting terminal member 013, from which current is collected by the current collecting rod 012. On the upper surface of the lead film 034, an airtight film (Al2O3) 035 with high airtight properties is formed. A cap-like sealing member 037 is bonded to the airtight film 035 via an inorganic adhesive 036. A similar sealing structure is provided for the outer peripheral surface near the upper end, beside the aforementioned tube sheet 04, of the substrate tube 031. The airtight film 035 is minimally porous as indicated by its porosity of about 5 to 10%, and thus prevents an escape of gas. Moreover, the airtight film 035 has a relatively large thickness of about 100 to 150 xcexcm to prevent oxidation of the lead film 034 located underneath.
The actions of the tubular type solid electrolyte fuel cell module with the foregoing structure will be described. The interior of the cell chamber 01a of the module body 01 is heated to an operating temperature (about 900 to 1,000xc2x0 C.). A fuel gas 020 such as hydrogen is supplied through the external pipe 07, while air 021 as an oxidant gas is supplied through the air supply pipe 018. The fuel gas 020 fed through the external pipe 07 flows from the fuel supply chamber 05 to the lower end of the cell tube 010 via the injection pipe 011. On the other hand, the air 021 that has passed through the partition plate 016 via the air preheating chamber 017 flows into the cell chamber 01a. The fuel gas 020 permeates through the porous substrate tube 031, and is fed to the fuel electrode 032a of the unit cell film 032. Whereas the air (oxygen) 021 contacts the air electrode 032c. At this time, the unit cell film 032 reacts the hydrogen and the air (oxygen) electrochemically to generate power. This power is transmitted to the outside via the current collecting member 013, current collecting rod 012, current collecting member 013, and conductive rod 014. A residual fuel gas 022 remaining after power generation flows into the fuel discharge chamber 06 from the upper end of the cell tube 010, and is discharged to the outside via the internal pipe 08 for reuse. Residual air 023 remaining after power generation is discharged to the outside via the air discharge pipe 019.
The above-described cell tube 010 has so far been laborious to produce, because the fuel electrode 032a, electrolyte 032b, and air electrode 032c are sequentially formed as films on the surface of the substrate tube 031 by means of a thermal spray gun 040 as shown in FIG. 7(A). Moreover, there has been a raw material loss 041 during film formation owing to the spraying of raw materials from the thermal spray gun 040, and the production cost has been high. Thus, a low cost for mass production has been desired.
Under these circumstances, a proposal has been made for a sintering process performed by forming films of raw materials for the fuel electrode, etc. sequentially on the surface of the substrate tube 031, followed by sintering films 042 thereon, as shown in FIG. 7(B). However, an airtight film of a cell tube obtained by the sintering process, as compared with that obtained by the thermal spraying process, has few asperities on the surface because of the sintering action. As a result, the airtight film is poorly sealable with the sealing member when sealed via an adhesive. The reason behind this phenomenon is as follows: As shown in FIG. 6, the airtight film 035 obtained by the conventional thermal spraying process comprises coarse particles, and has surface roughness of about 10 to 15 xcexcm, thus ensuring satisfactory sealability with the adhesive. By contrast, the airtight film obtained by the sintering process has very low surface roughness of about 2 to 5 xcexcm because of the sintering action. Consequently, adhesion to the adhesive is not satisfactory, and may result in a leak.
In light of the above-described problems, the present invention aims to provide a sealing structure of a sinter type cell tube for a tubular type fuel cell, the sealing structure designed to increase the sealability of the cell tube, thereby enhancing the electrical characteristics of the fuel cell.
A first aspect of the invention is a sealing structure of a cell tube for a fuel cell, the cell tube comprising a unit cell film prepared by forming a fuel electrode and an air electrode as films on a surface of a substrate tube for the fuel cell by a sintering process, with a solid electrolyte being interposed between the fuel electrode and the air electrode, wherein:
an adhesion enhancing film having a predetermined roughness characteristic is included in a sealed portion of the cell tube between an air tight film and a sealing member.
Thus, adhesion to the adhesive can be enhanced to decrease a gas leak. Furthermore, formation of the cell tube by the sintering process results in a marked increase in the utilization factor of the raw materials, as compared with the thermal spraying process. Besides, the production facilities are simpler with the sintering process. Thus, the equipment cost and the production cost can be reduced markedly.
In the first aspect of the invention, the sealed portion of the cell tube may be composed of a conductive lead film formed on the surface of the substrate tube, and an airtight film with high airtight properties formed on a surface of the lead film;
the adhesion enhancing film is located on a surface of the airtight film; and
a sealing member is formed on a surface of the adhesion enhancing film via an adhesive coated on the surface of the adhesion enhancing film.
Thus, adhesion to the adhesive is enhanced to decrease a gas leak.
In the first aspect of the invention, the adhesion enhancing film includes a rough surface with surface roughness characteristic of 10 xcexcm or more. Thus, adhesion to the adhesive is enhanced to decrease a gas leak.
In the first aspect of the invention, the adhesion enhancing film has a porosity of 5 to 30%. Thus, adhesion to the adhesive is enhanced to decrease a gas leak.
In the first aspect of the invention, the adhesion enhancing film comprising a film of, or a mixture of, CaTiO3, MgAl2O4, calcia-stabilized zirconia, and yttria-stabilized zirconia. Thus, adhesion to the adhesive is enhanced to decrease a gas leak.
In the first aspect of the invention, the adhesion enhancing film has a film thickness of 20 to 30 xcexcm. Thus, adhesion to the adhesive is enhanced to decrease a gas leak.
The airtight film has a porosity of 3% or less. Thus, the gas barrier properties of the film is improved. Moreover, adhesion to the adhesive is enhanced to decrease a gas leak.
The airtight film has a film thickness of 60 to 100 xcexcm. Thus, the gas barrier properties of the film is further improved. Moreover, adhesion to the adhesive is enhanced to decrease a gas leak.
A second aspect of the invention is a tubular type solid electrolyte fuel cell module which supplies an oxidant gas and a fuel gas to a cell tube comprising a unit cell film formed on an outer peripheral surface thereof in a cell chamber in an environment at an operating temperature, to react the oxidant gas and the fuel gas electrochemically, thereby obtaining a power, wherein:
the above-described sealing structure of a cell tube for a fuel cell is used.
This module adopts a fuel cell system with markedly increased sealability. Thus, there is an increase in the utilization factor of residual fuel in a bottoming cycle of a gas turbine or the like. Consequently, an improvement is achieved in the electrical efficiency of a fuel cell combined power generation system using a gasification furnace, etc.
A third aspect of the invention is a method for producing a cell tube for a fuel cell, comprising:
forming an adhesion enhancing film by a sintering process simultaneously with forming a fuel electrode and an electrolyte as films on a substrate tube by sintering; and
then forming an air electrode by sintering.
Thus, the adhesion enhancing film achieving a decrease in the gas leak is formed.
A fourth aspect of the invention is a method for producing a cell tube for a fuel cell, comprising:
forming a fuel electrode and an electrolyte as films on a substrate tube by sintering; and
then forming an adhesion enhancing film by sintering simultaneously with the forming of an air electrode as a film also by sintering.
Thus, a denser adhesion enhancing film achieving a decrease in the gas leak is formed.
A fifth aspect of the invention is a method for producing a cell tube for a fuel cell, comprising:
forming an adhesion enhancing film by sintering simultaneously with the forming of a fuel electrode, an electrolyte, and an air electrode as films on a substrate tube also by sintering.
Thus, the unit cell film and the adhesion enhancing film is formed simultaneously by a single sintering step. This is an efficient method.